I told her we live together and are committed, and if things get better we will get married. But she has hinted she doesn’t want to wait, and that she might leave. To me, how does that make sense?
It doesn't. It is not logic speaking. It is emotions.

How do you respond to this? Not emotionally, you use logic. Example: Coming up with your list of what you require in a relationship. But boundaries in place so that you have clear understanding of how you will behave when they get crossed. This has nothing to do with her and everything to do with you.

"What is best for my kids is best for me"
Amor Fati
Link to quotes: https://www.divorcebusting.com/forums/ubbthreads.php?ubb=showflat&Number=2879712